Implantable nerve electrode and method for producing an implantable nerve electrode

ABSTRACT

The invention relates to an implantable nerve electrode ( 1 ) that comprises an electrically insulating substrate ( 2 ) with conductor traces ( 3 ) running therein, electrode contacts ( 4 ) and connection contacts ( 5 ), wherein the conductor traces ( 3 ) connect the electrode contacts ( 4 ) to the connection contacts ( 5 ), and wherein the electrode contacts ( 4 ) can be connected to the nerves of a nervous system, each of the conductor traces ( 3 ) having an at least partial sheathing ( 13 ) made of a polymer that is mechanically strong and a good insulator. The invention further relates to a method for producing an implantable nerve electrode ( 1 ).

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of International ApplicationNo. PCT/EP2012/063463, filed on Jul. 10, 2012, which claims priority toU.S. Provisional Patent Application 61/475,763, filed Jul. 11, 2011, thecontents of each of which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to an implantable nerve electrode according to thepreamble of claim 1 as well as to a method for producing such animplantable nerve electrode.

BACKGROUND

Functional electrical stimulation restores for many patients havingimplanted devices, as for example, pacemakers, defibrillators, bladderstimulators, implants for coping with pain, tremor, epilepsy and forrecovering the sense of hearing, body functions which have been lost.For this, implantable nerve electrodes are applied.

In prior art, it is known to produce implantable nerve electrodes bymeans of laser treatment from medical silicone and a metal foil. Thebasis of the known process is the separation of conductive paths andcontact areas from a metal foil typically 5 to 25 μm thin by means of alaser. The conductive path, electrode and contact areas are embeddedinto medical silicone, whereby the single signal paths may be isolatedelectrically from each other. The contact areas subsequently are exposedby means of the laser.

This known technology, however, has two problems: The conductive pathsare extremely fragile due to their fineness. The elastic silicone mayonly protect them to a very limited extend from mechanical influences,as, for example, while handling during the implantation. Accordingly,laser processed nerve electrodes, on the one hand, are relatively proneto breakage of conductive paths. On the other hand, silicone has a lowelectric strength. When a stimulation is carried out by means of nerveelectrodes electrically, voltages of several 10V between two adjacentconductive paths may occur. According to manufacturer specifications,the electric strength of silicone may be lowered to 2 kV/mm by storingit in water. A voltage of 20 V between two adjacent conductive pathswith a distance of 10 μm, thus, may lead to an electrical break down.This fact limits the integration density of the electrode.

In order to solve the problem of the inadequate stability, it is knownin prior art to, for example, arrange the conductive paths in meanderinglines. Hereby, a certain extensibility of the conductive paths isachieved. However, the increased space requirement is disadvantageousfor the meandering arrangement of conductive paths, which in turn has anegative impact on the maximum integration density.

A further approach involves the embedding of conductive paths in thickerand harder silicone. However, also this variant has little success,because also thicker silicone is much more elastic than the metalembedded therein. The occurring mechanical forces further influence theconductive paths substantially, and lead to their damage.

It also has been attempted to increase the mechanical stability byadding a polymer foil which is mechanically very strong and a furthersilicone layer, which have been inserted into the multi-layer structureof silicone-metal-silicone. Hereby, an improvement of the mechanicalstability of the nerve electrode may, however, be achieved, but the newmulti-layer structure silicone-metal-silicone-polymer-foil-silicone isunfavorable in that the layer of the rigid polymer foil which isnon-compressible or non-extendable defines the mechanically neutralfiber within the multi-layer structure. With strong bending movements,therefore, compressional or tensile forces of the metal conductive pathsoccur.

With respect to the second problem of the low electrical strength of thesilicone in which the conductive paths are embedded, up to now noapproach to a solution has been found.

Therefore, it is an object of the present invention to provide animplantable nerve electrode and a method for producing a nerve electrodeaccording to which an effective protection for the conductive paths andat the same time a high integration density may be achieved.

SUMMARY

This object is solved by an implantable nerve electrode having thefeatures according to claim 1, and by a method for producing a nerveelectrode having the features according to claim 10. Preferredembodiments of the invention are specified in the respective dependentclaims.

According to the invention, an implantable nerve electrode is providedhaving an electrically insulating substrate with conductive pathsrunning therein, electrode contacts and terminal contacts, wherein theconductive paths connect the electrode contacts to the terminalcontacts, and wherein the electrode contacts are connectable to nervesof a nervous system, wherein each of the conductive paths has an atleast partial jacket made from a mechanically rigid and electricallywell insulating polymer. Because each conductive path within thecomposite silicone-metal-silicone is sheathed individually by amechanically rigid and electrically well insulating polymer at leastpartially, on one hand, the disadvantages with respect to theinsufficient mechanical stability of the conductive paths may beovercome. On the other hand, a high integration density can be achieved,because the jacket insures a good electrical insulation. By means of theconfiguration according to the invention, the mechanically neutral fiberlies within the plane of the metal, whereby also with high bendingloads, no compression or extension of the conductive paths occurs. For apatient, whom a nerve electrode will be implanted, by the highmechanical stability, a higher reliability of the implant can besecured. Also, the electrical insulation between the single conductivepaths of the nerve electrode allows a further miniaturization of thestructure to be introduced into the body of the patient, as well as alsothe implementation of complex systems with high integration density.

According to a preferred embodiment, the mechanical rigid andelectrically well insulating polymer from which the jacket is made,comprises parylene, in particular parylene C, polyethylene orpolypropylene. These materials have an electrical strength 100 timeshigher than a silicone which has been used up to now. In particular,parylene C has an electrical strength of 220 kV/mm, allowing asubstantially improved integration density of the conductive paths.

According to a further preferred embodiment, the conductive paths, theelectrode contacts and the terminal contacts are made from a laserstructured metal foil. The production of the conductive paths, electrodeand terminal contacts by means of laser enables a specifically wellreproducibility and a high degree of automation.

It is especially preferred, when each single conductive path has anindividual jacket. This configuration offers a specifically effectiveprotection of the fragile conductive paths.

Preferably, each of the conductive paths is covered completely by ajacket, which even further enhances the protection of the conductivepaths.

According to a further preferred embodiment, the mechanically rigid andelectrically well insulating polymer is present additionally between theconductive paths. Hereby, a mechanical enforcement of the nerveelectrode may be implemented specifically locally.

Preferably, the conductive paths being sheathed by the mechanical rigidand electrically well insulating polymer are embedded in silicone, inparticular, in medical silicone, in particular, polydimethylsiloxan,which forms the electrically insulating substrate of the implantablenerve electrode.

According to a further preferred embodiment, the jackets made from themechanically rigid and electrically well insulating polymer areconnected to each other, in order to form the electrically insulatingsubstrate of the implantable nerve electrode. With this it isadvantageous that further layers, the silicone layers, may be omitted.The production method of such a nerve electrode, thereby, is simplifiedaccordingly, and thus, is cheaper.

Moreover, it is advantageous, if the conductive paths, the electrodecontacts, and the terminal contacts are made from stainless steel orfrom platinum.

According to the invention, a method for producing an implantable nerveelectrode is provided, whereby the method comprises the following steps:Providing a mechanical support: Applying a non-stick coating to theupper surface of the mechanical support (if necessary), applying a firstsilicone layer onto the upper surface of the mechanical support,laminating a metal foil being coated on one side with the first layer ofa mechanically rigid and electrically well insulating polymer, whereinthe coated side of the metal foil faces the first silicone layer,structuring the metal foil by means of laser in order to exposeconductive paths, electrode contacts and terminal contacts, applying acover layer made from the mechanically rigid and electrically wellinsulating polymer onto the structured metal foil, wherein the coverlayer connects to the first layer made from a mechanically rigid andelectrically well insulating polymer. By means of the inventive method,the advantages described above are achieved. In particular, hereby anerve electrode having an improved mechanical stability and a higherintegration density of the conductive paths may be produced. Theinventive production process, moreover, enables a locally definable and,if needed, an isotropic rigidity of the nerve electrode, which may beadapted to the respective application.

According to a preferred embodiment, the method further comprises thestep of structuring the cover layer by means of laser.

According to a further preferred embodiment, the method furthercomprises the step of applying a second silicone layer, in particular,thin-coating of the liquid silicone onto the structured cover layer.

According to still a further preferred embodiment, the method furthercomprises the step of curing the second silicone layer.

Preferably, the method further comprises the step of exposing theelectrode contacts and the terminal contacts by means of laser.

According to a further preferred embodiment, the method furthercomprises the step of defining the outer contours of the implantablenerve electrode by means of laser.

Preferably, the method further comprises the step of separating by meansof laser the defined implantable nerve electrode from the support.

According to a further preferred embodiment, the non-stick coatingcomprises a PVC foil, in particular, Tesafilm.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the invention will be further describedwith reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of an implantable nerve electrode accordingto prior art;

FIGS. 2 a to 2 p are respective sectional views of a sequence of methodsteps of a method for producing an implantable nerve electrode accordingto an embodiment of the invention; and

FIGS. 3 a to 3 n are respective sectional views of the sequence ofmethod steps of a method for producing an implantable nerve electrodeaccording to a further embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective view of an implantable nerve electrode 1according to prior art. The nerve electrode 1 comprises an electricallyinsulating substrate 2, which here is medical silicone, into which theconductive paths 3 are embedded. The conductive paths 3 connectelectrode contacts 4 to terminal contacts 5.

FIGS. 2 a to 2 p are respective sectional views of the sequence ofmethod steps of a method for producing an implantable nerve electrodeaccording to an embodiment. In FIG. 2 a, the first method step isillustrated, in which a non-stick coating 7, as e.g., self-adhesive PVCfoil, as for example, Tesafilm, is applied onto a mechanical support 6,which for example consists of glass or ceramics. In the second step,illustrated in FIG. 2 b, a first silicone layer 8 of liquid siliconebeing only a few 10 μm thin is spin-coated onto the upper surface 9 ofthe support 6 which is already provided with the non-stick coating 7,and is cured subsequently. Thereafter, as shown in FIGS. 2 c and 2 d, ametal foil 10, which in the embodiment has a thickness of 12.5 μm and ismade from platinum, and which is provided on one side with a first layer11 from a mechanically rigid and electrically well insulating polymerbeing only a few μm thick, in the embodiment parylene C, is laminatedonto the first silicone layer 8. In the subsequent step, which isillustrated in FIG. 2 e, the metal foil 10 is structured by means of alaser such that a metal, which later on will not serve as conductivepaths 3, electrode or terminal contacts (4, 5; see FIG. 1) may beremoved, as is visible in FIGS. 2 f and 2 g. Then, as is illustrated inFIG. 2 h, the cover layer 12 being only a few μm thick and alsoconsisting of parylene C, is applied which connects to the first layer11 (FIG. 2 i), and for each conductive path 3, an individual jacket 13is formed. In the next step, which is illustrated in FIG. 2 j, theexternal contours of the subsequent parylene layer, namely, the coverlayer 12 are structured with a laser and the excessive parylene isremoved (FIG. 2 k). In a further laser step, which is illustrated inFIG. 21, the cover layer 12 is removed at the locations of thesubsequent electrodes, illustrated here is the terminal electrode 5. Byspin-coating of a second silicone layer 14, which only is a few μmthick, and subsequent curing, the conductive paths 3 sheathed withparylene are completely embedded in silicone. By means of a laser, thenthe openings for electrode and terminal contacts, illustrated here isthe terminal contact 4, are cut into the silicone (FIG. 2 n), and theexternal contours of the nerve electrode 1 are defined. Due to the pooradhesion between silicone and the non-stick coating 7, now the nerveelectrode 1 may be separated from the mechanical support 6, as isvisible in FIG. 2 o. In FIG. 2 p, eventually, the nerve electrode 1,which is produced at the end of the production procedure, is shown.

However, according to a further embodiment it is also possible to omit acoating with a second silicone layer 14. Then, hereby, the method stepsshown in FIGS. 2 i and 2 j are carried out such that all conductivepaths 3 are mechanically connected to each other via their jackets 13from parylene C, and only the external contour of the nerve electrode isdefined into the polymer by means of laser cuts. According to the methodstep shown in FIG. 21, then the electrode and terminal contacts areexposed by means of laser, and a finished nerve electrode 1 may bepulled off from the first silicone layer 8. The nerve electrode 1, thusproduced, has according to this production procedure conductive paths 3and electrode and terminal contacts 4, 5, which are embedded into asubstrate from parylene C.

FIGS. 3 a to 3 n are respective sectional views of the sequence ofmethod steps of a method for producing an implantable nerve electrode 1according to a further embodiment according to which the conductivepaths 3 are only partially covered with a mechanically rigid andelectrically well insulating polymer, here also parylene C. By this, asimplification of the production method is achieved, and it is enabledto implement an electrical opening “downwards” as will be obvious in thefollowing. The method steps illustrated in FIGS. 3 a and 3 b correspondto the ones in FIGS. 2 a and 2 b, and therefore, will not be repeatedlydescribed. In the step illustrated in FIG. 3 c, the edges of thesubsequent electrode openings are processed by means of laser, as isshown by reference numeral 15. Then, as shown in FIG. 3 d, a metal foil10 is laminated onto the first silicone layer 8, which subsequently iscut by means of a laser, such that the areas not required as conductivepaths 3, electrode or terminal contacts 4, 5 (see FIG. 1) are removed(FIGS. 3 e, 3 f, 3 g). Subsequently, parylene C is applied to thesurface in a planar manner to form a partial jacket 13 for theconductive paths 5 (FIG. 3 h). In FIG. 3 e, the next step isillustrated, in which the layer from parylene C is structured by meansof laser such that undesirably coated areas subsequently may be freedfrom parylene C (FIG. 3 j). Subsequently, a silicone layer 14 is applied(FIG. 3 k), which is cured and then is processed such that (FIG. 31)electrode and terminal contacts facing “upwards”, here the terminalcontact 5, are exposed and the external edge of the nerve electrode 1 isdefined. For completion of the production method, the mechanical support6 is removed (FIG. 3 m) such that the finished nerve electrode 1 isobtained (FIG. 3 n).

LIST OF REFERENCE NUMERALS

-   1 nerve electrode-   2 electrically insulating substrate-   3 conductive path-   4 electrode contact-   5 terminal contact-   6 support-   7 non-stick coating-   8 first silicone layer-   9 upper surface of the support-   10 metal foil-   11 first layer-   12 cover layer-   13 jacket-   14 second silicone layer-   15 edge

What is claimed is:
 1. Implantable nerve electrode (1), which has anelectrically insulating substrate (2) with conductive paths (3) runningtherein, electrode contacts (4), and terminal contacts (5), wherein theconductive paths (3) connect the electrode contacts (4) to the terminalcontacts (5), and wherein the electrode contacts (4) are connectable tonerves of a nervous system, wherein each conductive path (3) has an atleast partial jacket (13) from a mechanically rigid and electricallywell insulating polymer.
 2. Implantable nerve electrode (1) according toclaim 1, wherein the polymer comprises parylene, in particular paryleneC, polyethylene or polypropylene.
 3. Implantable nerve electrode (1)according to claim 1, wherein the conductive paths (3), the electrodecontacts (4), and the terminal contacts (5) are made from a laserstructured metal foil (10).
 4. Implantable nerve electrode (1) accordingto claim 1, wherein each single one of the conductive paths (3) has anindividual jacket (13).
 5. Implantable nerve electrode (1) according toclaim 1, wherein each of the conductive paths (3) is covered completelyby the jacket (13).
 6. Implantable nerve electrode (1) according toclaim 1, wherein the polymer is present between the conductive paths (3)additionally.
 7. Implantable nerve electrode (1) according to claim 1,wherein the conductive paths (3) sheathed by a polymer are embedded insilicone, in particular in medical silicone, in particular inpolydimethylsiloxan, which forms the electrically insulating substrate(2) of the implantable nerve electrode (1).
 8. Implantable nerveelectrode (1) according to claim 1, wherein the jackets (13) from thepolymer are connected to each other, in order to form the electricallyinsulating substrate (2) of the implantable nerve electrode (1). 9.Implantable nerve electrode (1) according to claim 1, wherein theconductive paths (3), electrode contacts (4), and terminal contacts (5)are made from metal, in particular, from stainless steel or fromplatinum.
 10. Method for producing an implantable nerve electrode (1)wherein the method comprises the following steps: providing a mechanicalsupport (6), applying a non-stick coating (7) onto an upper surface (9)of the mechanical support (6), applying a first silicone layer (8) ontothe upper surface (9) of the mechanical support (6), laminating a metalfoil (10) being coated on one side with the first layer (11) from amechanically rigid and electrically well insulating polymer, wherein thecoated side of the metal foil (10) faces the first silicone layer (8),structuring the metal foil (10) by means of a laser in order to exposeconductive paths (3), electrode contacts (4), and terminal contacts (5),applying a cover layer (12) from a polymer onto the structured metalfoil (10), wherein the cover layer (12) connects to the first layer (11)from polymer.
 11. Method according to claim 10, which further comprisesthe step of structuring the cover layer (12) by means of laser. 12.Method according to claim 10, which further comprises the step ofapplying the second silicone layer (14), in particular, spin-coatingliquid silicone onto the structured cover layer (12).
 13. Methodaccording to claim 10, which further comprises the step of curing thesecond silicone layer.
 14. Method according to claim 10, which furthercomprises the step of exposing the electrode contacts (4) and theterminal contacts (5) by means of laser.
 15. Method according to claim10, which further comprises the step of defining the outer contours ofthe implantable nerve electrode (1) by means of laser.
 16. Methodaccording to claim 10, which further comprises the step of separatingthe implantable nerve electrode (1) defined by means of laser from thesupport (6).
 17. Method according to claim 10, according to which a PVCfoil is used as non-stick coating (7).
 18. Method for producing animplantable nerve electrode (1), in particular according to claim 1,wherein the method comprises the following steps: providing a mechanicalsupport (6), applying a non-stick coating (7) onto an upper surface (9)of the mechanical support (6), applying a first silicone layer (8) ontothe upper surface (9) of the mechanical support (6), laminating a metalfoil (10) being coated on one side with the first layer (11) from amechanically rigid and electrically well insulating polymer, wherein thecoated side of the metal foil (10) faces the first silicone layer (8),structuring the metal foil (10) by means of a laser in order to exposeconductive paths (3), electrode contacts (4), and terminal contacts (5),applying a cover layer (12) from a polymer onto the structured metalfoil (10), wherein the cover layer (12) connects to the first layer (11)from polymer.